Building block pen



FIG. 1 is a front perspective view of a building block pen showing mynew design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a right side view thereof, a left side view not being shown asit is a mirror image of the right side view;

FIG. 5 is a rear view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

CLAIM The ornamental design for a building block pen, as shown and described. 